(1) Field of the Invention
The present invention relates to the exercise of quality control over a packaging process and particularly to the non-destructive testing of the degree of filling of cigarette papers and packages. More specifically, this invention is directed to optical test apparatus and especially to reflectivity measuring devices for testing the degree of filling of cigarettes and the completeness of blocks of cigarettes which are to be wrapped as individual packages. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
Optical test apparatus for use in the measurement of the degree of filling of cigarette papers are well known in the art. One such prior art device is shown in U.S. Pat. No. 4,267,444 which is assigned to the assignee of the present invention. In the appartus of this patent a transceiver has its light emission and collection surfaces arranged transversely to the axes of the cigarettes to be tested, these surfaces being separated from one another by a neutral zone. The emission and collection surfaces cooperate with a fiber optic plate on which the cigarette ends are brought to rest. The light emitted by the test apparatus is transmitted to the cigarettes and, after multiple reflections in the region of each cigarette, a portion of the emitted light will impinge upon a collector. Due to losses along the light path, the intensity of the light received at the collector is greatly reduced when compared to the emitted light. The intensity of the light received by the collector is inversely proportional to the number of the tobacco fibers which are present. Accordingly, if a pre-selected threshold value of received light intensity is exceeded, the cigarette under test is taken to be a reject. Apparatus of this type has the disadvantages of being technically complex and relying upon a low level signal as an indication of an acceptable product. Since the collector may see stray light, and the surface on which the cigarettes are supported during testing may become soiled, use of a low level signal as an indication of an acceptable product is very disadvantageous.
It is also to be observed that the apparatus of the aforementioned German patent is characterized by output signals from the photocells of the collectors which rise to a peak value at an intermediate point along a plot of distance versus reflected light intensity and then decrease. Accordingly, the signals provided by the collectors are subject to ambiguity. For example, if the end of a cigarette in a block is spaced a relatively great distance from the testing head as a result of breakage, the reflected signal will lie on the decreasing side of the illumination curve and may be within the range which is indicative of an acceptable cigarette.
For a further description of the prior art, reference may be had to application Ser. No. 444,315 entitled "Mechanism for the Testing of the Degree of Filling of Cigarette Ends" which has been filed contemporaneously with this application.